Fix non-termination issue in sygus enumerator (#8340)

Fix non-termination issue in sygus enumerator (#8340)

This ensures that the sygus enumerator does not get stuck in rare cases.

In particular this is important when doing PBE and one of the enumerators (among return/condition enumeration) is out of values. This ensures we break when we fail to increment an enumerator for a type that is required to validate a child enumerator.